Polycyclic addition polymers having directly linked polycyclic repeating units without any internal backbone unsaturation are desirous from the standpoint of their inherent thermal oxidative stability and high glass transition temperature (Tg) profiles. Recent objectives in synthesis have focused on incorporating pendant functional substituents onto the polycyclic backbone, enabling this class of polymer to be utilized for a wide variety of uses. These objectives have been successfully met in part because of the advent of late transition metal catalysts and their tolerance to functional groups. An increasingly important use for such polymers has been in the manufacture of microelectronic and optical devices. An important consideration in the manufacturing of polymers for microelectronic and optical applications is polymer purity. While specific classes of transition metal catalysts are tolerant to functional groups, there is a trade off in that monomer to catalyst ratios must be high in order to overcome the poisoning effects of the functional group on the catalyst. Consequently, many polymers contain metallic residues as a result of the high catalyst loading in the reaction medium. Traces of transition metals have been shown to catalyze the thermal oxidative degradation of polymers. In addition, metal residues in the polymer also deleteriously affect the polymer properties by raising the dielectric constant of the polymer and interfere with light transmittance through the polymer matrix. In order to be useful the residual metals must be removed from the polymer to below an acceptable level.
One method of catalyzing the polymerization of cycloolefins is through the use of cationic transition metal complexes. Goodall et al. (U.S. Pat. No. 5,569,730) describe a method for polymerizing cycloolefinic monomers such as norbornene and hydrocarbyl substituted norbornene-type monomers in the presence of a chain transfer agent and a single or multicomponent catalyst system capable of providing a Group VIII transition metal cation source. The preferred single component catalyst consists of a transition metal cation complex containing an allyl ligand and a weakly coordinating counteranion. The multicomponent catalyst system employs a Group VIII transition metal ion source, an organoaluminum compound and an optional component selected from Lewis acids, strong Brρnsted acids, electron donor compounds, and halogenated organic compounds. The monomer to Group VIII transition metal molar ratios are broadly disclosed to range from 1000:1 to 100,000:1, with a preferred range of 3000:1 to 10,000:1.
Goodall et al. (U.S. Pat. No. 5,705,503) and McIntosh et al. (WO 97/20871) disclose that norbornene-type monomers containing functional substituents can be successfully polymerized with single and multicomponent transition metal catalysts of the classes disclosed in the '730 patent supra. However, the molar ratio of monomer to Group VIII transition metal ranges from 20:1 to 100,000:1. In fact the highest monomer to Group VIII metal ratio actually employed is only about 5000:1 which is exemplified in Example 15 of the '503 specification.
In addition to the Group VIII single and multicomponent catalyst systems disclosed supra, Goodall et al. (WO 97/33198) disclose a single component catalyst system suitable for polymerizing functionally substituted norbornene-type monomers. The single component catalyst comprises nickel, a two electron donor ligand (preferably a π-arene ligand) and a pentafluorophenyl ligand. The disclosed molar ratio of monomer to nickel ranges from 2000:1 to 100:1.
In view of the foregoing it is apparent that a relatively high catalyst loading (based on the Group VIII metal content) is necessary for the polymerization reaction to proceed efficiently. A higher catalyst loading in the monomer at the onset of the polymerization reaction, however, means that a higher residual metal content will be present in the polymer product. Residual metals are difficult and expensive to remove. Therefore there is a need for a high activity transition metal catalyst system capable of polymerizing substituted and unsubstituted cycloolefin monomers.